Mobile devices may be equipped with satellite based navigation systems for determining position and providing navigation assistance. A global navigation satellite system (GNSS) such as, for example, the Global Positioning System (GPS) may send timing signals used by mobile devices to estimate the position of the mobile device. However, in some situations mobile devices may be unable to receive the satellite timing signals. For example, when a mobile device is indoors, in a canyon, in the shadow of tall buildings, or other environment that may block satellite signals. In such circumstances, sensor equipped mobile devices can perform pedestrian dead reckoning (PDR) to estimate the mobile device's position. However, accuracy is limited by magnetic disturbances inside structures, sensor precision, and other unknown variables such as device position, bias, and differences in stride. Additionally, PDR error from use of mobile device sensor data is typically magnified over time as every new positioning error is compounded with previous errors.
As an alternative to GNSS or PDR, mobile devices may determine positions by leveraging a predetermined reference map containing WiFi access point locations. The mobile device can determine its position by trilateration (i.e., referencing at least three separate WiFi access points) of WiFi signal strength and/or ranging to known values within the predetermined map. However, WiFi location information and predetermined reference maps may not always be available or reliable. Therefore, there is a need for a standalone, real-time positioning system run on the mobile device.